Commercial lithium ion batteries (LIB) nowadays can provide an energy density of more than 200 Wh/kg, but manufacturers are continuing to search for ways to raise the energy density further to meet the increasing power consumption needs of mobile electronics and electric vehicles. Developing new anode materials with capacity exceeding the theoretical capacity of graphite (i.e. 372 mAh g−1) is a challenge. Numerous studies to replace graphite with other materials such as post-transition elements and their oxides were reported intensively. Metal sulfide is another category of materials that potentially give high capacity. However, these materials tend to show low capacity, low first cycle efficiency as well as poor stability.
While LIB have been the main energy storage medium for mobile applications for the past 20 years, sodium ion batteries (NIB) are now becoming to be seen as an alternative to LIB because of the lower costs and larger abundance of sodium, This has therefore recently attracted much attention. One of the main obstacles to the commercialization of NIB is the limited choice of anode materials that can provide good stability and high rate performance. Commercialization of LIB was mainly driven by the ability for lithium to intercalate into graphite, resulting in large and stable capacity. As opposed to lithium, sodium cannot be intercalated into graphite.
Therefore, there remains a need to provide for alternative anode materials for LIB and NIB to overcome, or at least alleviate the above problems.